1. Field of the Invention
The invention relates to compositions for orally administering paclitaxel and related taxanes to human patients, and methods of treatment employing such compositions.
2. Description of the Prior Art
Many valuable pharmacologically active compounds cannot be effectively administered by the oral route to human patients because of poor or inconsistent systemic absorption from the gastrointestinal tract. These pharmaceutical agents are, therefore, generally administered via intravenous routes, requiring intervention by a physician or other health care professional, entailing considerable discomfort and potential local trauma to the patient and even requiring administration in a hospital setting with surgical access in the case of certain IV infusions.
One of the important classes of cytotoxic agents which are not normally bioavailable when administered orally to humans are the taxanes, which include paclitaxel, its derivatives and analogs. Paclitaxel (currently marketed as TAXOL® by Bristol-Myers Squibb Oncology Division) is a natural diterpene product isolated from the Pacific yew tree (Taxus brevifolia). It is a member of the taxane family of terpenes. It was first isolated in 1971 by Wani et al. (J. Am. Chem. Soc., 93:2325, 1971), who characterized its structure by chemical and X-ray crystallographic methods. One mechanism for its activity relates to paclitaxel's capacity to bind tubulin, thereby inhibiting cancer cell growth. Schiff et al., Proc. Natl. Acad. Sci. USA, 77:1561–1565 (1980); Schiff et al., Nature, 277:665–667 (1979); Kumar, J. Biol. Chem., 256: 10435–10441 (1981).
Paclitaxel has been approved for clinical use in the treatment of refractory ovarian cancer in the United States (Markman et al., Yale Journal of Biology and Medicine, 64:583, 1991; McGuire et al., Ann. Intern. Med., 111:273, 1989). It is effective for chemotherapy for several types of neoplasms including breast (Holmes et al., J. Nat. Cancer Inst., 83:1797, 1991) and has been approved for treatment of breast cancer as well. It is a potential candidate for treatment of neoplasms in the skin (Einzig et al., Proc. Am. Soc. Clin. Oncol., 20:46), lung cancer and head and neck carcinomas (Forastire et al. Sem. Oncol., 20:56, 1990). The compound also shows potential for the treatment of polycystic kidney disease (Woo et al, Nature, 368:750, 1994) and malaria.
Paclitaxel is only slightly soluble in water and this has created significant problems in developing suitable injectable and infusion formulations useful for anticancer chemotherapy. Some formulations of paclitaxel for IV infusion have been developed utilizing CREMOPHOR EL™ (polyethoxylated castor oil) as the drug carrier because of paclitaxel's aqueous insolubility. For example, paclitaxel used in clinical testing under the aegis of the NCI has been formulated in 50% CREMOPHOR EL™ and 50% dehydrated alcohol. CREMOPHOR EL™ however, when administered intravenously, is itself toxic and produces vasodilation, labored breathing, lethargy, hypotension and death in dogs. It is also believed to be at least partially responsible for the allergic-type reactions observed during paclitaxel administration, although there is some evidence that paclitaxel may itself provoke acute reactions even in the absence of Cremophor.
In an attempt to increase paclitaxel's solubility and to develop more safe clinical formulations, studies have been directed to synthesizing paclitaxel analogs where the 2′ and/or 7-position is derivatized with groups that would enhance water solubility. These efforts have yielded prodrug compounds that are more water soluble than the parent compound and that display the cytotoxic properties upon activation. One important group of such prodrugs includes the 2′-onium salts of paclitaxel and docetaxel, particularly the 2′-methylpyridinium mesylate (2′-MPM) salts.
Paclitaxel is very poorly absorbed when administered orally (less than 1%); see Eiseman et al., Second NCI Workshop on Taxol and Taxus (September 1992); Suffness et al. in Taxol Science and Applications (CRC Press 1995). Eiseman et al. indicate that paclitaxel has a bioavailability of 0% upon oral administration, and Suffness et al. report that oral dosing with paclitaxel did not seem possible since no evidence of antitumor activity was found on oral administration up to 160 mg/kg/day. For this reason, paclitaxel has not been administered orally to human patients in the prior art, and certainly not in the course of treating paclitaxel-responsive diseases.
Docetaxel (N-debenzoyl-N-tert-butoxycarbonyl-10-deacetyl paclitaxel) has become commercially available as TAXOTERE® (Rhone-Poulenc-Rorer S. A.) in parenteral form for the treatment of breast cancer. To dates no reference has been made in the scientific literature to oral absorption of docetaxel in animals or patients.
It has been speculated that, in some cases, the poor or non-existent bioavailability of a drug such as paclitaxel after oral administration is a result of the activity of a multidrug transporter, a membrane-bound P-glycoprotein, which functions as an energy-dependent transport or efflux pump to decrease intracellular accumulation of drug by extruding xenobiotics from the cell. This P-glycoprotein has been identified in normal tissues of secretory endothelium, such as the biliary lining, brush border of the proximal tubule in the kidney and luminal surface of the intestine, and vascular endothelial cells lining the blood brain barrier, placenta and testis.
It is believed that the P-glycoprotein efflux pump prevents certain pharmaceutical compounds from transversing the mucosal cells of the small intestine and, therefore, from being absorbed into the systemic circulation. A number of known non-cytotoxic pharmacological agents have been shown to inhibit P-glycoprotein, including cyclosporin A (also known as cyclosporine), verapamil, tamoxifen, quinidine and phenothiazines, among others. Many of these studies were aimed at achieving greater accumulation of intravenously administered cytotoxic drugs inside tumor cells. In fact, clinical trials have been conducted to study the effects of cyclosporine on the pharmacokinetics and toxicities of paclitaxel (Fisher et al., Proc. Am. Soc. Clin. Oncol., 13: 143, 1994); doxorubicin (Bartlett et al., J. Clin. One. 12:835–842, 1994); and etoposide (Lum et al., J. Clin. One. 10:1635–42, 1992), all of which are anti-cancer agents known to be subject to multidrug resistance (MDR). These trials showed that patients receiving intravenous cyclosporine prior to or together with the anti-cancer drugs had higher blood levels of those drugs, presumably through reduced body clearance, and exhibited the expected toxicity at substantially lower dosage levels. These findings tended to indicate that the concomitant administration of cyclosporine suppressed the MDR action of P-glycoprotein, enabling larger intracellular accumulations of the therapeutic agents. For a general discussion of the pharmacologic implications for the clinical use of P-glycoprotein inhibitors, see Lum et al., Drug Resist. Clin. One. Hemat., 9: 319–336 (1995); Schinkel et al., Eur. J. Cancer, 31A: 1295–1298 (1995).
In the aforedescribed studies relating to the use of cyclosporine to increase the blood levels of pharmaceutical agents, the active anti-tumor agents and the cyclosporine were administered intravenously. No suggestion was made in these publications that cyclosporine could be orally administered to substantially increase the bioavailability of orally administered anti-cancer drugs and other pharmaceutical agents which are themselves poorly absorbed from the gut without producing highly toxic side effects. None of the published studies provided any regimen for implementing the effective oral administration to humans of poorly bioavailable drugs such as paclitaxel, e.g., indicating the respective dosage ranges and timing of administration for specific target drugs and bioavailability-enhancing agents are best suited for promoting oral absorption of each target drug or class of drugs.
In published PCT application WO 95/20980 (published Aug. 10, 1995) Benet et al. disclose a purported method for increasing the bioavilability of orally administered hydrophobic pharmaceutical compounds. This method comprises orally administering such compounds to the patient concurrently with a bioenhancer comprising an inhibitor of a cytochrome P450 3A enzyme or an inhibitor of P-glycoprotein-mediated membrane transport. Benet et al., however, provide virtually no means for identifying which bioavailability enhancing agents will improve the availability of specific “target” pharmaceutical compounds, nor do they indicate specific dosage amounts, schedules or regimens for administration of the enhancing or target agents. In fact, although the Benet et al. application lists dozens of potential enhancers (P450 3A inhibitors) and target drugs (P450 3A substrates), the only combination of enhancer and target agent supported by any experimental evidence in the application is ketoconazole as the enhancer and cyclosporin A as the target drug.
When describing the general characteristics of compounds which can be used as bioenhancers by reduction of P-glycoprotein transport activity, Benet et al. indicate that these are hydrophobic compounds which generally, but not necessarily, comprise two co-planar aromatic rings, a positively charged nitrogen group or a carbonyl group—a class that includes an enormous number of compounds, most of which would not provide the desired absorption enhancing activity in the case of specific target agents. Moreover, the classes of target agents disclosed by Benet et al. include the great majority of pharmaceutical agents listed in the Physicians' Desk Reference. These inclusion criteria are of no value to medical practitioners seeking safe, practical and effective methods of orally administering specific pharmaceutical agents.
In general, Benet et al. provides no teaching that could be followed by persons skilled in the medical and pharmaceutical arts to identify suitable bioenhancer/target drug combinations or to design specific treatment regimens and schedules which would render the target agents therapeutically effective upon oral administration to human patients. Benet et al. also provides no direction whatsoever regarding how paclitaxel and other taxanes might be administered orally to humans with therapeutic efficacy and acceptable toxicity.
In published PCT application WO 97/15269, which corresponds to U.S. patent application Ser. No. 08/733,142 (the grandparent of the present application) and which 10 is commonly owned with this application, it is disclosed that various therapeutically effective pharmaceutical “target agents” which exhibit poor oral bioavailability can be made bioavailable, providing therapeutic blood levels of the active agent, by oral co-administration of certain bioavailability enhancing agents. Preferred examples of such target agents disclosed in WO 97/15269 include the cyclosporins, e.g., cyclosporins A, D and G. Preferred examples of target agents include the taxane class of antineoplastic agents, particularly paclitaxel. Therapeutic regimens and dosage amounts for co-administration for target agents and enhancing agents are also disclosed. All of the disclosures of published application WO 97/15269 are incorporated herein by reference.
Neither commonly owned application WO 97/15269 nor any prior art disclosure, however, describes classes of oral formulations or compositions containing the active target agent, e.g., paclitaxel, which are particularly adapted for co-administration with an oral bioavailability enhancing agent to yield therapeutic blood levels of target agents heretofore considered unsuitable for oral administration.